Method of heat-treating steei



NT" eras can eerie WALTER C. PETERSON, OF DETROIT, MICHIGAN.

METHOD OF HEAT-TREATING STEEI No Drawing.

T all'whomit may concern:

Be it known that I, a citizen of the United States, and residing at Detroit, Vayne county, State of Michihave invented certain new and-useful Improvements in Methods of Heat-Treating Steel, of which the following is a speci L fication.

' critical point before quenching in order to refine or harden the same. After the steelhas been heated above the critical point, if it is cooled slowly there is a point where the temperature remains'constant but heat is given out by the steel. This point is termed the recales'cence point andmay be from 85 F. to 215 F. lower than the deca-lescence point. p

When a steel article is hardened in the manner outlined above, its dimensions are changed by the treatment so that they are not the same as prior to the hardening and the changes in dimensions have not been uniform. Thus after the heat treating the article may be Warped, or slightly larger or smaller than the dimensions of the same after machining; or the changes in dimenslons may be certain comblnations of the three changes mentioned. Of course according to the present invention the treatment of the steel articles is such that in.

- their final'form there is no warping and the size is exactly that required. For this reason it has been necessary to perform an machining operation on the article afterbeing hardened, inorder to bring it to therequired dimensions. It is one of the prineipal objects of the present invention to elirriinate this machining operation. To this end,

the steel is heat treated in such a manner that after hardening it assumes, the dimensions required. a

I have discovered the factthat if a steel is heated to a certain predetermined tem- Speeificaticn of Letters Patent.

WALTER C. Pnrnnson,

Patentedalune 7, 11921.

Application filed May 19, 1919. Serial No. 298,348.

perature above the critical point at a cer-' tain rate and then quenched it will assume the same dimensions as prior to the heating.

The proper temperature and rate to which the steel is heated to accomplish this result vary with the different compositions. of steels and consequently no general rule for determining their value can be given. The temperature and rate must be determined by experiments performed on each different kind of steel.

It' is believed that steel while being heated up to the quenching temperature, expands from the time it begins to 'b eheated during which time it contracts. After leaving the decalescence zone itexpands until quenched when it contracts once more. T he two sets of forces thus set up in the process of heating and quenching a piece of steel are governed in magnitude by the rateat which the steel is heated. In other words,

it is believed, that when the steel is being heated and is at its critical temperature, it

contracts; and if the heating is continued to such a temperature above the critical temperature, that the expansion due to this heating above the critical "temperature is equal to the contraction occuring during the critical point, then the steel "when quenched will assume its original dimensions;

The present invention is of particular value in manufacturing .steel wheels, such as gears used in the change geartra'nsmis- SIOIIS of motor vehicles.

Such gears are subjected to severe shocks and clashing and must be made with the object of standing up under such service. The complete process for manufacturing and heat treating steels to form gears for this service may be as follows:

1st: The steel is forged from 2,000 F;

-dow'n to 1600 F. to formthe blank.v

' I 2nd The blank is then heatedto 1650 F. and quenched in a liquid. I

3rd:' The blank is again heated to 1550 F. and then cooled slowly to anneal the same. These last two steps refine'and equal-- "ize the internal structure of the gear so that there are no hard or soft spots.

4th: The blank is now machined to the required dimensions.

5th: The machined article is heated to a temperature above the critical point and quenched in oil. 5

to the time it enters ,the decalescence zone" (quenched; i 5 determined after the 'gar experiment; and is such that he same as W; en firstfma- Forflthe]purp ose' 'of; illustrating the ternperatures to which the article is heated-in steps-5 and '6',{these-temperatures Willbe in-t dicated'for. a particular steel. A steel hav ing the. follotvin'gj composition has been found very satisfactory: v g

1 Carbon .45 to 255% Manganese" .30 1.50 Phosphorus underf i025. a Sulfurng under 1.040 a Silicon under-.25-

N 1.50 to-2.00% Chromium .90 to l.10

After a blank o flthis steel has been 'forged-.. and machined, the temperature toivhich it is heated instep. 5 i s11500? F.,' and the tern-4 perature to which it. is heated in step. ti-is] 1420" Ff Preferably," the heating'in both 'instances-is-atsuch a rate'as 'to' raise the? article; substantially 30 's ameyheating again to a predetermined temperatureaboveiits critical point ataprd 5 determined rate but lower than the. previous temperature of the F. per minute, a

Although the invention has" been described in connection With a particular steel, it isto be understood that the invention is notthus limited but is applicableto other steels. Having thus described the invention What is claimed as new anddesired to-be secured by Letters Patent is:'

' a 1. In a process of treating being such v that thei article after i being quenched assumes the same dimensions as previous to the heating.

the steps consisting in machining a blanlr to the desired' dimensions, "heating the artlcle thus formed to a predetermined tempera} ture above its criticalpoint at a predetermined rate and thenquenching, saidtemperature and rate beingsuchthat the artisame cle after being quenched assumes the dimensions as when machined.

3. The process of treating steel articles consisting in macl'iining a blank to the desired dimensions, heating the article thus formed to a temperature above its critical.

point, quenching, heating again to a predetermined temperature above its critical point at a predetermined rate but lower than the previous temperature, and then cle has been uenched, its-'- to. a predetermined temperature above .its' critical point at'a predetermined rate and then quenching, said temperature and rate" 2. In a process of treating steel articles quenching, said predetermined temperature andrate being such: that the article after being-'.'quenched :assumes' the same dimensiohs as when machined 4. The process of treati1ig- Jst eel articles I consisting in heating the article to a 'preder termined temperature, above" its critical point at a predetermined rate and'cquen'chc nsisti'ng in, giving ablanlca preliminary treatmentto refine 1t, machining theb-lank -to the desired dimens1ons,fheat1ng the arm-'- ole thusmade to a predetermined tempera 9 mined rate and. quenching, said temperaturefif ture above its critical pointat "a predeter- '70 ing," said-temperature and-rate being such and rate being such that the expansion of the. critical point/ The process Sf-{treating steel articles consisting in, giving a; blank a prelimi'nary -the article when beingfheated above the, critical point-equals the contractionwhile at treatment to refine it,"m achining the blank to the desired dimensions, heating thejarticle thu'sfm'ad'e' to ateniperature above its critical point and quenching to harden the heating and quenching, the temperature and rate of the second heating being :such that the article after beingf'quenchedassumes the same dimensions; as when machined. i

,. a The process of treating steel"-articles steel articles the steps 'consi'stinginheating the articleformed to a temperature above its'critical point; andquenching to hardenthe same,

- again heating the'article to a temperature aboveits critical point but lower than the previous temperature at a rate of approximately 30. F. per minute and then quenching, saidllast mentioned temperature and rate being such that the article after being quenched'a'ss'umes the same dimensions as When machinedr I v In a process of. treatinglsteel articles the steps consisting in heating the article to a temperature of approximately 1500 F.-

and quenching to harden the v same, again heating the article {p'atemperature of approximately 1420" t, at a rate of substantially' 30 perminute and quenching,-said last mentioned temperature and rate being such that the article after being quenched assumes the same dimensions as at first.

In testimony whereof I affix my signature.

entries on PETERSGN. 

